This page is still actively being updated
The TeslaCycle (homemade electric moped)
Introduction to project
My goal here is to provide details about my electric moped project- which I like to refer to as the TeslaCycle. This was just a fun project I did out of curiosity, it's not pretty, well done or perfect in any way. It's a proof of concept, and a successful one. It's also not finished and I will continue to make updates to this page as I can.
Disclaimer- this is not a how to guide, and I am not a professional. Be safe.
Getting started- the bike
The moped I modified is one I bought a few years ago off Craigslist for $150. It was pretty trashed and I brought it home with the hope of getting it running and cleaned up. I worked on it for a while but the wiring and motor were pretty toast. I went ahead and cleaned up the frame and painted it. I did not realize at the time that I probably did something I shouldn’t have- I painted it yellow. At the time I didn’t realize that there was a different version of the PA50 that was originally yellow. So for the record, I didn’t paint mine yellow to try and pass it off for the better Hobbit. I know some people will be upset that I took such liberties with a collectible and classic moped. All I can say is that it’s now even more special.
Whenever working with lithium ion cells make sure you know what you’re doing and use proper safety measures. I am not a professional and I am not recommending that anyone repeat exactly what I’ve done- it’s not perfect.
I decided to build a battery out of individual lithium ion 18650 cells. At this point my battery is 100 cells- 10 Series 10 Parallel. This means that my pack has a nominal voltage of 37V and charges up to about 42V. Ideally it would be plenty to get me around but there are some issues with my battery that are causing me trouble as I discuss below.
Getting the Cells:
I got these cells out of used laptop batteries. For $50 I bought about 150 pounds of used laptop batteries at on online action. I then broke open the cases and removed the cells. Once the cells are pulled out you have to remove the metal tabs that will typically still be attached to the cell. Be careful not to short the cells when pulling them off.
Preparing the Cells:
Since I was using used cells I had to determine which ones were worth using and which were truly trashed. I measured the voltage of each cell and typically only kept cells that had at least 2.5V. This ended up being about half the cells. For reference- most of the laptop batteries had 6 or 9 individual cells in them. I then used a combination of two smart charges to test each cell. The chargers I used each hold 4 cells at a time. The problem is it takes about 12 hours to run a full test. This is a time consuming process, but necessary if you want to ensure that you are only using cells that will provide a decent amount of energy. I kept any cells that were above 2 AH.
In my opinion this part sucks. I started by trying to spot weld the cells using a homemade spot welder. I used some online/youtube instructions to try and build a spot welder out of a 12v battery and a high current solenoid, but all I managed to do was blow holes through the nickle strips. I didn’t want to solder the tabs as it’s not recommended so I ended up settling on a kit sold by Vruzend. If I was doing this again, I would have used the more expensive kit they cell since it is designed for higher current draw. To build a battery out of 100 cells I had to buy two kits. Even with the kit it’s a pain in the ass.
I started by building a 24V battery out of 35 cells 7S5P but that didn’t provide enough power so I kept going.
Pro tip- if you build a similar Vruzend battery, make sure that you are conscious which way the tabs on the end face. If you want to add additional rows of batteries at a latter point, it is much easier if you’ve aligned the tabs in such a way that you can add more without having to disassemble the battery. I’ll provide more specifics soon.
BMS & Charging:
To be safe and not push the battery to unsafe limits I used a BMS module matched to the voltage of my battery- 36V. The BMS provides a number of safety features including low voltage cut off, over voltage protection and it also monitors each row of cells. These can be found online and are important if you’re building your own battery.
The good- the battery works and gets me moving. It charges up to 42V and provides enough power to get me moving pretty quickly. Plus it was cheap. I can pull about 20amps from the battery pack before voltage sags enough to cut out (BMS).
The bad- I have a problem with the voltage dropping under load and triggering the BMS to cutoff power due to low voltage. I have a voltmeter attached so I can monitor the real time voltage and it’s clear that when I ask for a lot of power all at once the voltage sags too much- down below 30V.
I will likely be building a completely new battery soon using better components- stay tuned.
This is another area where I will admit I am not using the best components. I used a 24V 500W electric motor that I already had from a previous project. This is a brushed motor. Most of the electric bikes/scooters I see now use brushless motors. Luckily it’s not going to be very difficult to upgrade my motor later on.
As I discussed above, I’m using a 36V battery and a 24V motor- this is not ideal, but it works. I don’t ride this bike very far at a time and the amount of heat that builds up is not very much. As I improve things on the bike I will eventually replace this motor with one that matches the battery.